Coastal Group

Introduction

The name Coastal Group is used for the various limestone, dolostones, impure limestones and clastics that were deposited around the margin of Jamaica during its tectonic uplift over the last 12-14 million years. These include both shallow-water and deep-water units.

It can generally be divided into an older part (mid/late Miocene to early Plesitocene) and a younger part (late Pleistocene).

In the northwestern part of Jamaica, the older part is referred to as the Hopegate Fomration (Pliocene) and contains abundant reef-building corals and is often dolomitized.

In the eastern part of the island, the olders part consist of several formations.
Manchioneal Formation and Old Pera Formation (Early Pleistocene).The former consists of nodular impure limestones, the latter of sandstones. Both contain abundant transported reef-building corals.
Layton Formation (late Miocene to Pliocene). This consists of marlstones and contains the famous Bowden Shell Bed at Bowden in St Thomas. The Layton Formation can be divided into three members (Buff Bay Member, San San Member, and Bowden Member) based on unconformities picked up from biostratigraphical studies.
Low Layton Formation - a succession of pillow basalts eruptedduring the transition from the White Limestone to the Layton Fomration at Black Hill in Portland.
August Town Formation (Miocene). A series of shallow-water impure limestones extending from Alligator Pond (Manchester) to Bowden (St Thomas).


The upper part of the Coastal Group is represented by the Falmouth Formation ('raised' coral reefs and associated lagoonal depoists) and Port Morant Formation (a disected fan delta).